The present invention relates to environmental control systems (ECSs), and more particularly to an air cycle machine (ACM) configuration.
ECSs provide a supply of conditioned air to an enclosure, such as an aircraft cabin and cockpit. Conventional ECSs have utilized an air-to-air cycle cooling system which is in a heat exchange relationship with a liquid loop. The liquid loop typically cools other heat loads such as avionics packages. Interaction between the air and liquid subsystems is relatively complex. Moreover, airflow sequencing, particularly for multi-turbine air cycle machines (ACMs), radically affects ECS efficiency. In many instances much thermal energy may be wasted or otherwise inefficiently used.
In one conventional system, a flow of bleed air is taken from an intermediate or high pressure stage within a jet engine. The bleed air is pre-cooled within an air-to-air heat exchanger with heat being rejected to RAM air and then flowed to a compressor of the ACM. After compression, the air is routed through a second air-to-air heat exchanger, a regenerative heat exchanger and an air-to-air reheater heat exchanger. Condensed water vapor is extracted by a water extractor, and dehumidified air is routed to a turbine. Expanded air from the turbine flows through another water collector and into a liquid-to-air heat exchanger of the liquid loop. A relatively warmer liquid in the liquid loop which is used to cool the avionics is thereby cooled. From the liquid-to-air heat exchanger, the air passes through the reheater heat exchanger. The dehumidified air is then passed into a second turbine of the ACM where it is again expanded and passed through another liquid-to-air heat exchanger to further absorb heat from the liquid loop.
The ACM is an integral part of the ECS. Conventional ACM's include at least two turbines and a compressor mounted along a common axis. The turbines and compressor are assembled using multiple shaft pieces and held together with a tie rod assembly. For example, the compressor may be mounted as a link between two shaft pieces. Typically, each shaft piece is machined to a desired tolerance in a separate operation and later assembled to the other pieces. Disadvantageously, the tolerances from each component compound in assembly. This often results in misalignment of journal bearing portions of the ACM and leads to undesirable shaft loads, vibration, and imbalance during ACM operation. Furthermore, conventional assemblies often require complex and heavy components to hold the shaft pieces, turbines, and compressor together, such as tie rods and robust static structures.
Accordingly, it is desirable to provide a simplified integral ACM rotor assembly that minimizes rotational loads.